1. Field of the Invention
This invention generally relates to an optical pick-up for use in an optical disk apparatus, and, in particular, to a tracking control device of such an optical pick-up.
2. Description of the Prior Art
In general, in an optical disk as an optical recording medium, various information is recorded on a surface by forming pits of approximately 1 micron in diameter at a pitch of approximately 2 microns on a recording track of the surface using a laser beam light spot. The recording track is defined in a pre-groove typically formed during manufacturing of an optical disk, and various information, such as identification information of a recording region and sync signal, necessary for proper management of recorded data is previously formed on the recording track. It is to be noted that such a recording track may be provided in plural number concentrically or singularly in a spiral format.
A laser beam is irradiated to the recording track of the optical disk and the light reflecting from the optical disk is picked up by an optical pick-up to thereby read the data recorded on the recording track. In such an optical disk apparatus, in order to read the information recorded on the recording track properly, it is required to position a light spot on the optical disk accurately. The proper positioning of a light spot on the optical disk can be attained by using a tracking control device. Such a tracking control device typically includes a phase compensation circuit for compensating the gain of a tracking servo loop. Typically, such a phase compensation circuit includes a delay phase compensation unit for compensating a control error (steady-state error) at a low frequency range and an advance compensation unit for securing stability of the tracking servo loop at intermediate and high frequency ranges.
In order to provide random accessibility in an optical disk apparatus, it is required for a light spot to jump from one track to another track radially of the optical disk. In accordance with the typical prior art method, such a track jump operation is carried out by turning the tracking servo loop off, then supplying a kick pulse for accelerating or decelerating a tracking actuator, and then turning the tracking servo loop on again. In such a prior art open-loop type pulse-driven track jump operation, it is susceptible to eccentricity of an optical disk and external disturbances, so that the positioning of the light spot after jumping tends to be unstable.